1. aEmail:- me143022@mnnit.ac.in bEmail:- rahuldsurya@mnnit.ac.in
PERFORMANCE ANALYSIS OF DIRECT EVAPORATIVE COOLER WITH FIN STRUCTURED PADS
Ashutosh Singha, Rahul Devb Department of Mechanical Engineering, Motilal Nehru National Institute of Technology Allahabad, Uttar Pradesh, India.
Abstract
Need for the Study
Results & Discussion
In our country, India, the most widely used appliance for cooling in summer is direct evaporative cooler because it is cheap. The most commonly used wetted media pads in such cooler is excelsior or wood wool pads as it is economical. Salt deposition and microbial growth is the major problem in such pads. This problem led to find some cheap and reliable solution for common people therefore fin-structured pads(FSPs) had been designed, which encounter the problems of excelsior pads satisfactorily when used along with it.
The mathematical correlation was verified by experimental data.
The efficiency of cooler with FSPs of width 80mm was found to be higher than the conventional cooler. The increase in efficiency varies from 9.7% to 11% and increase in temperature drop(tdrop) (difference between the inlet air dry bulb temperature and outlet air dry bulb temperature) varies from 0.8°C to 1.8°C under different inlet conditions i.e. %RH ranging from 23.8% to 50.1%, tdb ranging from 38.1°C to 38.6°C and twb ranging from 22°C to 31°C.
Theoretically with the help of the correlation, the efficiency and change in tdrop was found to increase as the pad width increases. For instance, for inlet condition tdb, twb and %RH as 38.4°C, 22°C and 23.8% respectively, the efficiency and tdrop increases from 55.5% to 75.1% and 8.9°C to 12.3°C respectively as the pad width increases to 150mm.
This study presents a new concept of increasing efficiency of Direct Evaporative Cooler by modifying its wetted media system.
A mathematical correlation is derived for theoretical analysis of fin structured pads.
Comparative study of direct evaporative cooler with and without fin structured pads is carried out
Fin-structured pads
Methods
These FSPs were made of cotton cloth because it is cheap and get wet easily.
The width of FSPs is 80mm (determined using mathematical correlation and size of cooler). Vertical fins were evenly attached at an interval of 1 cm (1 cm is so chosen because when the interval was kept less than 1cm then wet fins used to get stuck together).
The fins were attached at an angle of 7°(experimentally determined) to minimize the restriction to air flow.
A parallel pipe arrangement was made to keep these pads wet. These FSPs were hanged in front of wetted media pads.
For comparative study between the cooler with and without FSPs, the outlet air dry bulb temperature was recorded for the same inlet conditions (inlet air dry bulb temperature(tdb), inlet air wet bulb temperature(twb) and %RH) and this comparative study was done under different inlet conditions.
Mathematical correlation was derived to theoretically analyze the performance of FSPs.
Experimental Setup
Conclusion
These FSPs were found to be effective.
They increase the efficiency of the cooler and in this way saves energy and promote sustainable development.
They also act as compensator when the efficiency of ordinary pads decreases due to salt deposition & microbial growth.
The cost of these pads for 15'' (fan size) cooler is ₹300/- hence the solution presented is reliable and affordable for common people.
Variation of efficiency with humidity
Contact
References
Wu JM., Huang X., Zhang H., “Theoretical analysis on heat and mass transfer in a direct evaporative cooler”. Applied Thermal Engineering Vol.29, Pg.980,Yr.2009.
Koca RW., Hughes WC., Christianson LL. “Evaporative cooling pads: test procedure and evaluation”. Applied Engineering Agriculture Vol.7, Pg.485, Yr.1991.
Change in temperature drop by variation of pad width
Where
‘t1’ is the inlet air dry bulb temperature passing through the fin structured pads
‘t2' is outlet air dry bulb temperature
‘h’is convective heat transfer coefficient of air
‘ ’ is width of the fin pads
‘N’ is no. of fin pads
‘H’ is the height of fin pads (m)
‘m’ is mass flow rate of air (kg s-1)
‘Cp’ is specific heat of air
Variation of efficiency with change in pad width